Fluid sample introduction system for analytical equipment



March 30, 1965 c. H. EHRHARDT ETAL 3,176,128

FLUID SAMPLE INTRODUCTION SYSTEM FOR ANALYTICAL EQUIPMENT Original FiledJuly 13. 1959 2 Sheets-Sheet 1 A/IL/ Emwv/eeg March 30, 1965 c, EHRHARDTETAL 3,176,128

FLUID SAMPLE INTRODUCTION SYSTEM FOR ANALYTICAL EQUIPMENT Original FiledJuly 13, 1959 2 Sheets-Sheet 2 Fig. 2

Char/es E. Ell/hard) Warren h. Mael/er Henry M. Grubb IN VENTORS UnitedStates Patent 3,176,128 FLUID SAMPLE INTRODUCTION SYSTEM F0 ANALYTICALEQUIPMENT Charles H. Ehrhardt, Western Springs, Ill., and Warren H.Moeller, Chesterton, and Henry M. Grubb, Highland, Ind., assignors toStandard Oil Company, Chicago, Ill., a corporation of Indiana Originalapplication July 13, 1959, Ser. No. 826,757, now Patent No. 3,103,277,dated Sept. 10, 1963. Divided and this application June 29, 1962, Ser.No. 210,287

7 Claims. (Cl. 250-413) This invention relates to an improved method andmeans for introducing samples into analytical equipment. Moreparticularly, it provides a system for introducing such samples havingaccurately predetermined volumes and in a manner which entirely avoidscontamination from air and other materials.

This is a division of application Serial No. 826,757, filed July 13,1959, and entitled Sample Handling Capsule, now US. Patent No.3,103,277.

In various analytical devices, particularly in mass spectrometers, aliquid or gaseous sample under analysis must be introduced into thedevice in a manner which permits the virtually complete elimination ofcontaminating materials. Air is the most troublesome of these. Also, thesample must be of known volume, or at least of reproducibly constantvolume. These two requirements have heretofore imposed substantiallimitations on the accuracy of mass spectrometry, particularly when thesample undergoing analysis has a low volatility, and must be introducedin vapor form at elevated temperatures.

Various attempts of the prior art to solve the problem of introducingsamples of known volume and free from air or other contaminants have metwith little success and only limited approval. Various means such ashypodermic syringes and self-sealing diaphragms are useless at hightemperatures, to say nothing of their lack of precise volume control.Other sample introduction system,

featuring liquid metal diplegs or more advanced types tremely highaccuracy of the analytical equipment by eitecting sample introductionwithout contamination by air or other agents, and which introduces afluidsample of accurately predetermined volume.

Briefly, and in accordance with the invention, we en close the samplefor analysis in a sealed capsule'made of a metal which fuses or melts ata temperature below that at which the sample itself exhibits anysubstantial decomposition. This sealed capsule is introduced into an airlock from which air may be removed by such means as evacuation, and theintact capsule is then transferred to a second chamber or melting zonewhere the metal which encapsulates the sample is melted away, therebyreleasing the sample into the second chamber and into the analyticaldevice.

Exceptional precision in preparing a sample of known weight or volumecan be accomplished in accordance with our invention. It the metal tubeused in making the capsule has a bore of known internal diameter, and itthe tube has or is cut to a predetermined length, then the sample volumeis accordingly very accurately prede- "Ice termined. A reproducibilityof 20.5% in volume measurements, and :2% in overall analytical results,is readily attained. Moreover, sample volumes on the order of onemicroliter or less can be handled with this same accuracy, a degree ofperformance never before attainable insofar as we are aware.

The present encapsulation technique affords numerous other advantages.Primarily, contamination by air or other gases can be almost entirelyeliminated. Also, even the most volatile liquid samples can be storedfor long periods of time, and can readily be shipped for analysis whennecessary for referee samples or for cooperative research programs. Foruse with high molecular weight, i.e. high boiling samples, the presenttechnique has no peer; no liquid sealed valves and no fritted glassdiscs are employed, thus minimizing opportunities for sampledecomposition on catalytically active surfaces. Also, in contrast tomolten metal diplegs, there is no problem of sample holdup. Lastly, thetest sample is not exposed to any high temperatures whatsoever beforeactual melting of the encapsulating tube. Other advantages will becomeapparent as the description of the invention proceeds in detailhereafter.

The invention will be more fully understood by reference to the ensuingspecification in conjunction with the attached drawings wherein FIGURE 1shows a capillary tube made of a low-melting metal such as indium andwhich has its bore filled with a liquid test sample, in various stagesof (a) filling, (Z2) cold welding to size, and (c) the finished capsulein cross-section; and

FIGURE 2 is a diagrammatic representation of a high temperature sampleintroduction system in combination with the necessary evacuationapparatus for use with a mass spectrometer.

Turning first to FIGURE 1, FIGURE 1(a) shows a length of capillarytubing 1 made of low-melting metal which has been filled with the liquidsample 2 by capillary action.

The length, outer diameter and bore diameter of tube 1 may be of anydesired size to provide a fluid sample of suitable volume and sufficientaccuracy for analysis. Somewhat more convenience is realized with tubesof less than say one-half inch long, although precision and accuracy ofthe volume obtained is achieved with somewhat longer tubes. A suitabletube size may be a one inch length of tubing which has inside diameterof 0.010 and an outside diameter of about 0.040". Since the requirementof a constant volume sample imposes a similar requirement of constantinternal diameter, it is desirable that this dimension be held at asaccurate a tolerance as possible. Accordingly, drawn tubing of circularcrosssection is to be preferred. The internal diameter may be of anyselected dimension, but if the tube is to be filled completely with thetest sample by capillary action, then it is desirable to have the innerdiameter of suitable size to fill the tube by capillarity in areasonable length of time e.g. 0.050" ID. or less.

Metals used in making tube 1 are available in a wide range ofcompositions and have varied melting points. It is primarily necessaryhowever that the metal should have a melting point below that at whichthe sample begins to decompose to an extent which will interfere withsubsequent analysis. Either pure elements or alloys of various metalsmay be employed. A desirable metal should be relatively soft so that itcan be sealed by pinching or the like; it should be malleable so that itcan be easily drawn into tubing; and preferably it should have a lowvapor pressure so as not to contaminate analytical equipment. Also, itshould not oxidize too readily in air at room temperature, so that itcan form a metal-to-metal neeessar'y.

bond by the process of cold welding when pressure is applied toadjoining surfaces. Cold welding is a common property of all metals,provided there be no major surface contaminants. and that the appliedpressure be suf-' ficiently great to cause metal-to-metal contact. Coldwelding, which is also termed self welding or contact welding, isrealized easily at temperatures within about 7 200 C. of the metalsmelting point.

Another requirement of the metal is that it not be reactive with thesample fluid at its melting temperature. This consideration somewhatlimits the range of usable metals with certain samples, e.g. halogenatedorganic compounds, but numerous metals are available which aresufliciently inert at their melting points.

.abeut ijo C., and accordingly more chemically resistant materials maybe preferred in this service. Tin is of value where the sample isnormally a solid, and melts at a temperature above the melting point ofindium.

An extensive listing of the chemical and physical properties of"individual elemental metals and their various alloys is compiled in thebook Liquid Metals Handbook, by Richard N. Lyon, published by the AtomicEnergy Commission and the Department of the Navy, second edition(revised), January 1954, especially chapters 2 and 3.

Among the elemental metals which have melting points 7 below anarbitrarily selected 250 C., there may be mentioned: the alkali metals,especially lithium (M.P. 179

. 4 sealing a hollow tube 1 in an atmosphere of the test gas. If the gasis refrigerated and liquefied, it may be convenient to employ gallium(M.P.+30 C.) or indium-tin eutectic as the encapsulating metal.

In obtaining liquid-illed capsules, tube 1 may be sealed either underthe surface of the liquid or, especially if 7 tube 1 has a sufficientlysmall bore, away from the bulk C.) indium, gallium (30 C.), mercury (39C.), tin

(232 C.), e'tc. The above book lists the composition and melting pointsof numerous low melting alloys, primarily made up of various proportionsof bismuth, lead, tin, cadmium, mercury, and antimony, with more or lessminor amounts of such metals as thallium, copper, zinc, etc.

Illustrative alloys include one of 16 weight percent tin, 21.5 indium,and 62.5 gallium, which melts at 10.7" C., ranging through Woods metal(M.P. 65.5 C.), Lipo- -witz alloy (MQP. 70 C.), Roses metal (M.P. 100C.),

etc.

As mentioned previously, indium tubing is ideal for the I presentprocess. Not only does it have the requisite chemical and physicalproperties for most analytical work,

but its vapor pressure is exceedingly low, which is of importance whenconducting mass spectrometic analyses at elevated temperatures, e.g.above about 200 C.

' Turning once again to FIGUREI, tube 1 may be filled with liquid sample2 by any suitable procedure. It is preferred to'employ an open endedtube and fill the same by capillary action, thereafter place the tube onan anvil or cutting block 3 and pinch remote portions thereof togetherby means of a pair of dies 4 and 5, which are spaced at a known distanceapart and which are caused. to move toward anvil 3 thereby pinching andsealing off a length of tube 1. In FIGURE 1(c), a capsule is shown insection which consists of pinched tube 1, with its ends of the liquidsample.

It is also possible to obtain a gravimetric determination of samplequantity. Tube 1 is first weighed, and then filled with sample fluid.Its ends are then cold welded shut, and the tube then re-weighed.

Turning-now to FIGURE 2, an inletsystem is schematically shown which issuitable for introducing a capsule 6 into a mass spectrometer or similaranalytical device operated under high vacuum.

The device essentially comprises an evacuable gas lock 20, into whichthe capsule 6 is initially placed, a second or expansion chamber 7wherein melting of the encapsulating metal takes place and the sample isvaporized, and a conduit 12 leading via a molecular leak into theionization chamber '32 of conventional mass spectrometer 33. Massspectrometer 33 also includes magnet 34, analyzer tube 35, diffusionpump 36 with vacuum pump 37, and collector 38. 'The mass spectrometer isconnected to the usual preamplifier 39, amplifier 40, and suitablerecorder 41. The molecular leak is provided by orifice 42. Except asotherwise noted, all parts within the dashed enclosure 45 and gaslock 20are of temperature-resistive glass, eigrVycor or Pyrex. I

The detailed operation and construction of a device according to FIGURE2 is as follows: capsule 6 containing a fluid test sample is placed in'gas lock 20 and is carried by cover 21 by means of ferromagnetic clip25. 7 Cover 21 has a mating surface which is sealed to a correspondthequick-opening type. The second valve 13 has a female portion 14 of glasswhich is groundiand lapped'to mate with a movable portion 16. Movableportion 16 is activated byferromagneticarmature'17, made of soft iron orthe like, and which is wholly encased in the glass body of valve 13.-Valved conduit 18 may be evacuated by pumpout line 15 which leads todiifusion pump 43 and vacuum pump 44. Thus a magnet or current-carryingcoil placed around valve 1'3 can open or close this valve withoutobtaining access to the inside of the valve body.

From 'valve 13, a conduit leads into a second glass chamber 7, wherecapsule 6 is melted and the liquid sample therein is caused to evaporateand expand. Chamber 7 and valve 13 are placed within oven, not shown,which brings its temperature to a temperature sufficient to melt themetal of capsule 6 and volatalize the sample; valve 13 is hea'tedtoprevent condensation oflthe sample thereon. Alternative capsule meltingmeans include the passage of a high amperage current through thecapsule, in-

duction heating, and the application of a high intensity light beam tothe capsule.

sealed by cold welding, and containing or confining a a known quantityof sample 2.

Similarly, a relatively long tube may be filled by capillarity or othermeans, ,and then the ends thereof sealed. Then short portions of thesealedtube may be obtained by, re cutting using the apparatus shown inFIGURE 1 (b) to provide a plurality of separated or separable capsules,each containing a fluid sample of constant volume and I composition.

Gas samples may be pbtained and encapsulated by In a line from thesecond chamber 7 to an analytical device, there is disposed anadditional but optionalvalve 8, which is similar to valve 13 and has afemale part 9 and a movable portion 10 which is actuated by means ofmagnetic armature 11 and a steel magnet, not shown. Valve 8 may remainin the open position during the entire operation. From valve 8, line '12leads to the molecular leak and ionization chamber of a massspectrometer device 33. To employ the inlet systernlof FIGURE 2, capsule6 is clipped to cover 21 by means 'of/clip 25. Cover 21 is placed on gaslock 20 and is sealed by suitable vacuumtight surfaces as previouslydescribed. With valve 19 closed, a vacuum is pulled via line 24, and asimilar vacuum is pulled in a second chamber 7 with valves 8 and 13opened.

When the pressure in gas lock 20 is at as high a vacuum as is desired,valve 19 is opened and a magnet placed near magnetic clip 25. Clip 25opens, releasing capsule 6 which descends through valve 19, line 18, andangled valve 13 into chamber 7. The temperature in chamber 7 ispreferably only slightly above the melting point of the metal employedfor making capsule 6, and accordingly sufficient time is available toclose off valve 13. This temperature must, however, be sufiicient tovaporize the sample. Valve 19 may be closed any time after valve 13 hasbeen closed.

As the metal of capsule 6 rapidly melts and collects in the bottom ofchamber 7, the liquid sample originally in capsule 6 evaporates, therebyfilling the chamber 7 volume.

With valve 8 open, a vaporized portion of the sample passes via line 12to the analytical device. When scanning by the analytical device hasbeen completed, valve 13 is opened, permitting pumpout line 15 toevacuate expansion chamber 7 and connecting lines. The system is thenready for reuse.

The instant system has been described in connection with its use in massspectrometry. It will be apparent that its numerous advantages are oflike importance in other analytical systems wherein either accuratesample sizing and/ or freedom from air or contamination are essential ordesirable to the analysis. For example, in ultraviolet and in infraredanalyses, it is desirable to eliminate contaminants of all types, andaccordingly the inventive system is advantageously employed. Also in gaschromatography, where reproducibility of sample volumes and promptintroduction of a contiguous and compact slug or burst of the sample isdesirable, the instant invention is of exceptional utility.

From the foregoing presentation, it is evident that there has beenprovided an especially valuable technique for use in conjunction withmodern chemical and physical analysis procedures. By encapsulating aliquid or gaseous sample in a low-melting metal tube, the sample may beintroduced into an analytical device via a gas lock chamber, and may bethus introduced without encountering any 6 contamination from air andthe like. Moreover, the sample is of constant and reproducible knownamount, and errors arising from sporadic sample volumes may beeliminated entirely.

While the invention in its various aspects has been described withreference to particular embodiments thereof, it is apparent that theseare by way of illustration only. Accordingly, it will be understood thatmodifications and variations thereof will be apparent to those skilledin the art, and it is thus intended to embrace all such modificationsand embodiments as fall within the broad scope of the appended claims.

We claim:

1. The method of introducing a fluid sample into an analytical devicewhich comprises sealing said sample in an elongated tube made of a metalwhich is fusible at a temperature below that at which the sampledecomposes, introducing said sample-containing sealed tube into theanalytical device, and melting the tube whereby to release the saidfluid sample.

2. Method of claim 1 wherein said analytical device is a massspectrometer.

3. Method of claim 1 wherein said metal is indium.

4. The method of introducing a fluid sample of known amount into ananalytical device Without concurrently introducing air therein whichcomprises sealing said sample in an elongated tube made of a metal whichis fusible at a temperature below that at which the sample decomposes,introducing the sample-containing sealed tube into a gas lock of ananalytical device, removing air from said gas lock, transferring saidsample-containing sealed tube to a melting zone, and melting theelongated tube whereby to release said sample in said melting zone.

5. Method of claim 4 wherein air is removed from said gas lock byevacuation.

6. Method of claim 4 wherein said elongated tube is a capillary tube.

7. Method of claim 4 wherein said metal is indium.

References Cited in the file of this patent UNITED STATES PATENTS2,714,164 Riggle et a1 July 26, 1955 2,824,967 Kamen Feb. 25, 19582,852,683 Peters et al Sept. 16, 1958 2,882,410 Brobeck Apr. 14, 1959

1. THE METHOD OF INTRODUCING A FLUID SAMPLE INTO AN ANALYTICAL DEVICEWHICH COMPRISES SEALING SAID SAMPLE IN AN ELONGATED TUBE MADE OF A METALWHICH IS FUSIBLE AT A TEMPERATURE BELOW THAT AT WHICH THE SAMPLEDECOMPOSES, INTRODUCING SAID SAMPLE-CONTAINING SEALED TUBE INTO THEANALYTICAL DEVICE, AND MELTING THE TUBE WHEREBY TO RELEASE THE SAIDFLUID SAMPLE.